Methods, systems, and apparatus, including computer programs encoded on computer storage media, for implementing a resolver service. One of the methods includes: obtaining, from a blockchain, event data for a plurality of blockchain transactions associated with a plurality of decentralized identifiers (DIDs); storing the event data in a database; receiving a request for information associated with the event data, wherein the request comprises one or more account identifiers; identifying one or more DIDs respectively corresponding to the one or more account identifiers based on pre-stored mapping relationships between the one or more DIDs and the one or more account identifiers; and providing, from the database, event data for one or more blockchain transactions associated with the identified one or more DIDs.